Steering mechanism



A. V. CAMINO ETAL July 5, 1960 STEERING MECHANISM 4 Sheets-Sheet 1 Filed March 15, 1956 mmvroas v ANTHONY v. ammo y WALTER a. HOGAN FIG.

g WIJ/l- Q A TTORNEY July 5, 1960 A. v. cAMINQ ETAL 2,943,818

STEERING MECHANISM Filed March 15, 1956 4 Sheets-Sheet 2 59 78 T9 76 BI INVENTORS v ANTHONY V. CAMINO l 6 6 BY WALTER H. HOGAN July 5, 1960 A. v. CAMINO ETAL 2,943,818

STEERING MECHANISM 4 Sheets-Sheet 3 Filed March 15, 1956 FIG. 7b

Fl INVENTORS ANTHONY V. OAMINO BY WALTER H. HOGAN ATTORNEY y 5, 1960 A. v. CAMINO ET AL 2,943,818

' STEERING MECHANISM Filed March 15, 1956 4 Sheets-Sheet 4 IN VEN TORS ANTHONY V. CAMINO BY WALTER H. HOGAN ATTORNEY s 2,943,818 r srnnitnvo MECHANISM motor which has a large surplus of torque producing:

Anthony V. Camin'o, Cleveland, andWaltehHfI-Iogan,

' Olmstead Falls, Ohio; assignor's to'Cleveland Pneumatic Industries, In'c., a corporation of hiof' rileaT ar. 15., 1956, Ser. No. 571,842 1 Cl'aims. emu-50)" This invention relates to steeringmechanisrns and more particularlyto a steering mechanism adapted-torv use in the ground steering of aircraft and the-like.

. It is an important object of this invention to provide a steering mechanism capableof steering through essentially any, desired steering angle. i i i torque through. the entire range of steering.

,It isstill another object of this-invention to provide a steeringmechanism for use in aircraft which will provide 1 vibration damping forces which are not affected 1 by the angle of steering.

Itis still another object of this invention to provide a steering mechanism which permits. full swiveling without disconnecting any of the linkage.- v

'-It 1s still another object of this invention ,to provide av steering mechanism which eliminates the necessity of any power in the neutral position;

It is also sometimes necessary, and almost always desirable,;to provide full swiveling of the landing gear through 360"-' wherein the swiveling is accomplished by an ex-' ternalpower source such as a tractor. or the like.

feature is particularly desirable on shipboard aircrafit:

wherelit is necessary to maneuver the aircraft in very confined quarters. .A structure according to this invention permits the full swiveling of the landing gear without any disconnect mechanism. If the occasion should arise the steering mechanism could be used to power the landing gear for steering through a full 360 steering range.

Referring to the drawings, Figure 1 shows a conventional landing gear structure with the preferred steering mechanism installed thereon. The landing gear includes an upper telescoping member 1.6 adapted to be mounted on the framev of the aircraft and a lower telescoping member,.11 on whichfare journaled ground engaging wheels v I I t is another important objeet of thisinventionto pro-w vide a steering mechanism which will supply constant;

12., The upper telescoping member 10 is fixed againstrotation by its mounting on the frame of the aircraft and the lower telescoping member ll is arranged to permit free rotation relative to the upper telescoping member-10. A steering collar 13 is mounted on the upper telescoping member 10 for, rotation relative thereto and is connected to the lower telescoping member 11 by torque arms 14 which prevent relative rotation between the steering collar 13 and the lower telescoping member 11 while permitting relative axial motion therebetween. Suitable spring and damping means should be provided between the two telescoping members to absorb the impact shock of landing swivel hydraulic connections. and permits the useof rigid .Figurer2 isan enlarged cross section showing the struc tural detail of the steering mechanism per se;

Figure 3 is a longitudinal section taken along 3 -3 of Figures 4 and 5 are enlarged cross sections showing the structure and operation of the preferred distributor valve;

.Figure 6 is a composite longitudinal section of the distributor valve with some 'ofitheelements rotated into the plane of section in order to provide a clear understanding of the valve operation; and; w

and also resiliently support the weight of. the aircraft when it is on the ground. A preferred steering motor 16 is fixed tothe upper telescopingmember 10 and is adapted to rotate the steering collar 13 in a controlled manner and thereby steer the wheels 12.

Referring to Figures 2 and 3, the steering motor 16 includes a cylinder block 17 which is bolted between an. upper cover plate 18 and a lower cover plate 19 by bolt fasteners 21. The upper cover plate 18 is axially fixed. to the upper telescoping member 10 between a shoulder' 22 and a bearing member 23 and is rotationally fixed by a key 24. The lower cover plate 19 is radially supported on the steering collar 13 by a bearing 26 and the steering collar 13 is in turn radially supported on the upper tele-' scoping member 10 by the bearing 2-3 and a bearing 27.

A gland nut 28 is threaded onto the upper telescoping member 10 and serves the dual function of axially positioning the bearing '27 and therethrough the steering collar 13 as well as securing a gland member 29 against arshoulder 31 formed in the upper telescoping member Figures 7 a' throughflf are 'progresjsive schematic illusi trations. showing fthe"operation of the 'stee'ringmotoru In modern'aircraft the power steering mechanism; must be capable or: turning thesteerabl'e wheel through the full range offfsteering -when the airplane is stationary.

This is the most'severe torque requirement of the steering mechanism since the rubber of the tire scuifs on the ground under these conditions. In prior art steeringmechanisrnsthe torque 'efiiciency' of the landing gear reduces as the landing gear is turned away from theiieutral' position wherein the wheel is aligned with the major axis of the' jaircraft. Since the 'steering mechanism must be ca-' pablebf providing suflicient torque to turn the landing gear in the extremes of the steering range, this has been the condition which usually determines the sizing of the vention is capable of producing constant torque throughout'the; entire steering range so a smaller more .efiicient mechanism results and it is not necessary to provide a 10. The gland member 29 provides lateral support be tween the upper and lower telescoping members 10 and 11 while permitting axial motion therebetween. vThecylinder block 17 is formed with a plurality of cylinder ;1 bores 32 which are' adapted to receive cooperating sliding pistons 33. Each of the cylinder bores 32 and the corre-' sponding piston 33 cooperate to define a cylinder chamber 34 whichis adapted to receive pressure fluid which produces an axial force urging corresponding piston 33' along its axis toward the central axis as of the landing steering motor. The steering motor according to this ingear.

' A cam 37 is rotationally fixed relative to the steering collar 13 by a plurality of keys 38 and is axially fixed relative thereto between a spacer 41 and a ring gear 39 which in turn is positioned against the bearing 23. The

cam 37 is formed with a plurality of similar lobes 42 which are symmetrically arranged around the cam. In

the particular structure shown, there are six lobes 42 formed on the cam 37. However, the requirements of the particular installation are'controlling in the choosing of the number of lobes as will be discussed in detail later.

Patented July 5', 1960- This" Each-of the lobesprovides afirst radially extending ramp surfaces 43- and a second opposed radially extending ramp surface 44 which are connected at the outer end of the lobe by an outer transition convex surface 46. Each of the ramp surfaces is also joined to th'e adjacent ramp" surface of the adjacent lobe by an innertransitioncon cavesurface 47.

The cylinder block 17 isformed with an upper skip-t 48'. and a lower skirt 49 which extend inwardly: to'=a1posi'- thrust bearingsv 56 mounted on either end of thecross shaft 53 are positionedwithin the slots 51 so that a'ny lateralforce applied to the cross shaft 53' by the cam follower 54" isabsorbed by the walls of the slots- 51. Therefore, as :the pistons 33 move axially back'and forth withintheir. corresponding cylinder bores 32; no lateral T forces are. transmitted to the pistons which could cause-- wearjor. seal problems.

The cam followers 54- engage the cam 37 at circumferentially spaced points along the camm'ingsurface Sincethere are-six. lobes o'nthe cam shown in the diawings; the lobes are circumferentially spaced from each othenbyv6O Also since there are three-cylinder bores 32, pistonst33 and cam followers-54 the various propor'-- tionsshouldlbe arranged so that the'cam followers arecircumferentially spaced from each other by an angle of: which is one third ofthe angle between the lobes 42 The inclined ramp surfaces 43 and 44-a're formed so" that they each extend around the cam through an angle substantially equal to 20 andsothat the outer and inner transition surfaces 46 and 47 combine to'extend through 20; Therefore; at all times one of'thecam followers-will engage one of the inclinedramp surfaces 43 and. anothercarn follower will engage oneof' the ramp surfaces 44; By utilizing this arrangement it is possible to'provide steering torque in either. direction at any time. Whenever pressure fluid is supplied to the cylinder chamberr'34-lcorrcsponding to the cam follower-which is engaging one oftheinclined ramp surfaces'43 the'can'r follower will press against the inclined ramp surfaces-- wilLproduce a given amount of piston travel regardless of: the point of engagement between the ramp surfaces andcarn. followers 54. If. this is done a constant torque mechanism; results.

Adistributor valve assembly-80h connected'between thescylinderchambers 34 and a" source of pressure fluid irr..order to provide the successive pressurizing of the withiran'upperend plate SS-and. a lower end -plate 59 The ramp surfaces :43 and- 44--should"beformed- 4; 7 sure fluid line 67 is connected to the rectangular opening 71 in the valve rotor- 64: Therefore, a first zone 65 around the valve rotor is in communication with the first pressure line 66 and a second zone 70 within the slot 68 in the rotor is in communication with the second pressure line 67. The two zones 65 and 70 are isolated from each other by a sealingv engagement between the ends of the valve rotor andthe faces of the end plates fits into the central rectangular opening 71 in thev'alve rotor so that rotation of thevalve shaft 76'ca'uses p 86 cylinder chambers 34. The distributor valve is provided which are positioned opposite sides of' a spacer'57. I

These three elements are bolted together by'boltfas teners 62,- andlcooperate to/form a valvecavityC" in which is. positioned a valverotorz64; The valve rotor symmetrically, spaced. ports 72. one, of which is; con; nected to each-- of 1 the cylinder chambers 34- through separate pressure lines 73; The ports 72: are spaced from the central. axisof the valve so that they open into the zone 70*a's' the'slo'v68 ro'tatesinto registration with them or are opento the zone as'the case may be. The valve rotor 64 is formedwith lands 74 which have a width only slightly larger than the diameter of the ports 72 so that the ports are either in fluid communication with tlie 'zone'65'or' the zone ex'ceptingin the special case whe-r'e the individual port is being valved: from one zone to the other.

A valve shaft 76 projects through the lowerend plate 59 and is'formed witha rectangular end portion 77 which rotation of the'rotor. Agear 78"is'mounted at the lowerend of the valve shaft 76by means" of a nut fastener 79 and intermeshe's" with an idler gear 81 which'in interme'shes with a ringgear 39 fixed on thesteering collar13. Thus,- as the cam 37 and steering collar" 13"" rotate, the valve rotor 64 rotates in a synchronizeduflan' ner.- The gearing niust be arranged so that the valve rotor 64 rotates with an angular velocity six" timesthe will be used to distinguish between-individual'cylinders' and parts corresponding therewith. In' each of 'th'e'se figures a reservoir 81, apump" P-' used to provide the pressure for the actuation of'the'motor and a" control valve V' are schematically shown; The-arrows o'iiLtlie figures indicate the direction of rotation and of fiuidflow'i In -Fi'gure 7a'the various" elements are'in the position showrrin-Figure 2. Ifth'e'cam 37"is"toberotated in a" clockwise direction pressure fiuid" is supplied mthe-first pressure li ne-66by connecting this line to the pressure" sideof-pump' P "through the valve V. The pressure line" 67 is also connected to the reservoir 81 through the valveV-so that the zonea70"is connecte'dto the reservoir return and-the zone 65' is connected' to 'tlre source'of pressure fluiitnamely. the pump; Because the port"-72a is-in' communication withxthe' zone 65 I the cylindercham her- 34aisz: also, incommunicationrwiththe? pump; P.

Theport- 72c is inacommunicationzwith'.the reservoir 81"- so the cylinder chamberi34c isflalso in communication. with the: reservoir. At-the instant shown innFigure-7a, the cylinder chamber 346 is isolatedfromboth-the" reservoir 81 and the pump-P because the land '74 covers. the port 72b. Since the cam follower-54a is incontact with onev of the .first inclined ramp. surfaces 43 a force is produced on the cam 37 which rotates it in a clockwise direction. The cam follower 54c being in engagement withone ofthe.secondinclined'ramp surfaces 44'will be"'can1nied"radially to'the left as the cam 37 rotates in a'clockwise-direction ca1'1sing 'thefluid Wlthllf'lhe cyl? inder'cham'ber "340 to" flow to the reservoir return. Be

cause" the valve rotor- 64 is geared to the cam 37 i for in turn the pump as soon as .the'steering mechanism] rotates from the position of Figure 7a.

As rotation continues the elements-assume the position of Figure 7b at which time the cam follower 54a engages one of the inner transition-surfaces 47 and the cam follower 54b engages one of the inclined ramp surfaces 43.

The cam follower 540 is still in engagement with one-of" the ramp surfaces 44 so additional movement in a clock-' wise direction will bring it into contact with one of the transition surfaces 46. During therotation to the position shown in Figure 7b the valve rotor 64 has rotated to the position wherein the port 72b is in communication with the zone 65, theport 720 is in communication with the zone 70 within the slot 68 and the port 72a is isolated from both zones by the land 74. Therefore, the cylinder chamber 34c is in' communication with the reservoir 81, the cylinder 34b is in communication with the pump P and the cylinder 34a is' isolated from both the pump P and the reservoir 81. Since pressure fluid is supplied to the cylinderrchamber' 34b a force-will be developedon the cam 37 causingit to continue to rotate in a clockwise are in tion the valve rotor 64 rotates through a fullrevolution.

direction and fluid will be pumped out of the cylinder chamber 340 tothe reservoir 81 due to the piston movement caused by the engagement'of -the cam follower54c and one of the ramp surfaces 44. The fact. that -the' cylinder chamber 34a is momentarily isolated from both the reservoir and the pump will not cause difficulty because the piston and cam follower are in their dead center position. at this time so the piston is momentarily stationary. V

As soon as the elements move from the position of Figure 7b the cylinder chamber 34a is brought into communication with the reservoir 81 through the zone 70 within the slot 68. As rotation in a clockwise direction continues theelements assume the position shown in Figure 70 at which time the cam follower 540 is in engagement with one of the outer transition surfaces 46 and the cam followers 54b and 54a are in engagement with the ramp surfaces 43 and 44 respectively. Because the valve rotor 64 has rotated with the cam 37 the port 72a is now in communication with the reservoir 81-but the port 72b remains in communication with the pump P. Since the port 72b is still in communication with the pump the cylinder chamber 34b is still pressurized the cam 37 will continue to rotate in a clockwise direction. However, movement of the piston associated with the cylinder chamber 34a caused by engagement of the cam follower 54a with the ramp surface 44 caused fluid contained within the chamber to be pumped to the reservoir 81. When the elements reach the position of Figure 7d the cam follower 54b is in engagement with one of the inner transition surfaces 47 and the port 72b is isolated from both the pump-P and reservoir 81. In this position however the cam follower 540 is in engagement with one of the ramp surfaces 43 and the cylinder chamber 340 is in fluid communication with'pump P. Ofcour'se the cam follower 54a engages one of the ramp surfaces 44 and thecylinder chamber 34a is in fluid communication with the reservoir 81; A clockwise rotation of the cam 37 x and valve rotor 64 continues until the position of Figure 1 7e is reached at which time the cam follower 54a engages one of the outer transition surfaces 46 and the cam followers 54c and 54b engage the ramp surfaces 43 and 44 respectively. The distributor valve also provides com-' position of Figurejf is reached. At this time the cam follower 54c engagesone of the inner transition surfaces 47' while the cam followers 54a and 54b engageramp 7 At all times one of the cam followers 54 is in engagement with one of the'ramp'surfaces 43 and another of the cam followers 54 is in engagement with one of the ramp sur faces-44. Also, the distributor valve always connects the cylinder chamber 34' associated, withthe follower 54 en'- gaging one of the ramp surfaces 43' to the pressure line 66 and the chamber 34- associated with the cain'follower engaging the ramp surface 44 to the pressure line 67. Therefore, if the connection of the pressure line 66 and- 67 is reversed by the valve V so that the pressure line 67 use asthe control valve V is shown in the copending application of Walter H. Hogan, Serial No. 489,987, fi1ed February 23, 1955.

In the preferred embodiment a pressure sensitive relief 7 valve Rshould be provided between the valve V and the reservoir 81 to maintain a back pressure in the line con-- necting'the valve V to the reservoir 81 so that the cylinder chamber 34 connected to the reservoir 81 will always be under a back pressure. This will produce a positive force between the cam follower 54 associated with the cylinder chamber 34 which is connected to the reservoir 81 so that back lash or free play is automatically taken up; In one preferred embodiment the source of pressure fluid is at a pressure of approximately 3,000 lbs. per sq. in. and the reservoir return ismaintained at a pressure of approximately 300 lbs. per sq. in. Therefore, a differential pressure of 2700 lbs. per sq. in. is available w produce steering torque.

The valve V should also be arranged so that when power steering is not required the two pressure lines 66 and 67 are connected together. Preferably flow'restrictions of the orifice type 82 and 83 are provided in the ing the two pressure lines 66 and 67 are connected to-'.

gether by the valve V and the wheels tend to turn in a clockwise direction under shimmy conditions the cam 37 is turned in the same direction. This causes the piston.

33 associated with the cam followervengaging one of. the ramp surfaces 44 to move-to the left. This causes fluid to be pumped from'the corresponding chamber 34 r through the distributorjvalve 80, the pressure linea67;

valve V, pressure line 66 and back to the cylindercham ber 34 associated with the cam follower 54 engaging one of the ramp'sur'faces 43. 9 Because the ramp surfaces 43 and 44 are de'signed to give constant torque for steering the two pistons'33 associated with the cam followers engaging the ramp surfaces move with equal velocity but inopposite directions. Therefore, fluid pumped from one chamberf34 flows to the other through thejorifices 82 and 83 which resist this flow. and therefore resist the motionof the cam 37 wheels 12. When the shimmy is in the opposite direction the fluid flows between the same chambers 34in the opposite direction and the orifices 8 2.-

and 83 again cause a resistance to the motion.

A plate 75 may be mounted on the cover members 18 and 19 around the cam to totally enclose the steering motor and prevent dirt or other foreign matter from entering the mechanism. This permits the use Of 1 16 simplepiston-and'cylinder structure without wiper, gland or the like: c

1 I'n vthe: illustrated embodiment there are three cylinder-sfand sixficam lobes however, it should be understood that an 'op'timum design for aparticular installation* mightreqbire' more" cylinders, a: different number of=cam:lobes or'- a different height of cam lobe.- f nece"- sar y theacylinders'mayi be: circumferentially' spaced so that they engage spac'e'drampfsurfac'es" on the cam ratherthan an' adjacent ramp as shown in the drawing. It'

is-importanbzhowever,-to arrangethe proportions so that thecamifollowers always engage'opposedramp surfaces so that torque in' either directioncan be provided from For' instanceif five cylinders were used swiveled-through a full-360 ,to facilitate the groundhaudling of'the aircraft and itis not necessary to disconuect'tliesteering-motor as is the casein most previous-steeringsystemsi Although apreferred embodimentofthis invention is illustrated, -it-willb'e realized-that various modifications ofz the structural details'may be rnade' without departing from the mode of operation and the essence of the inventions Therefore, except insofar as'they are claimed in the 'appended-claims; structural detailsmay be varied widely without'modifying the mode of operation. cordingly, theappended' claims and not theaforesaid de taileddescript-ion are-determinative of the scope of the invention.

We claim:

l.- Anaircraft steering mechanism comprising a pair of me'rnbers'capableof relative rotation, a cam fixed on one of said members provided with a first group; of spaced ra'm p surfaces and asecond group of'spaced-opposed-ramp surfaces inclined in a manner whereby a linearforce'suppliedsuccessively to onegroup of surfaees causesrotation of said'one' member, a plurality of fluid motors mountedon-theotherof said members each first-fpressure line; a-iluid reservoir connected to a second pressure lineya-cam follower carried 7 by eachelement engaging.:.said cam ad'aptedto exert 'said linear force by virtue:of movement of said element, said cam and fluid mdtorsrbeingaproportioned so-that-at least one-cam follower always engages "one-ofisaid firstgroup of surfaces 'andwatleast-anotheralways engages one of said second ground-"surfaces;allofsaid rampsurfaces being formed sc -that"thefiratio:between-the magnitude of lineal-displacement of-- a cam follower engaging any ramp surface relative.;to the magnitude of the annular displacement ofsaid cam is aconstant; and control means operated by virtueof tiie rot" on offsaid one memberopei'ably connected to saidfluid motors toisuccessi'velyconnect' the fli'lid meter associated with the" cam follower engag- Acv including; an element movable underthe influence of pr'e'ssureifluid; a' source ofpr'essure fiuid connected to a one of said members provided with a plurality of space similar first ramp surfaces and second similar opposed ramp surfaces inclined in a manner whereby a linear force supplied successively to similar surfaces causes r0- tation" of said one member, a plurality of fluid'motors mounted ohthe other of said members e'achincluding an" element movable in response to pressure fluid,first'and second'fluid pressure lines, a cam follower carried by each element adapted to exert said linear force on'said surfaces by virtue of said movement of said element; said cam and fluid motors being proportionedso that at least one cam follower is alwaysin engagement with one ofsaidfirst surfaces and another always'in'engagement witli'one ofsaid second surfaces, all of said ramp surfaces beingiformed so that the ratio between'the' magnitude oflinea'r displacement of a cam follower engag ing any ramp surface relative to the magnitude of the annular displacement of said cam is a constant, and dis tributor means operated by virtue of the rotation of said one'member operably connected to said fluid motors to successively connect the fluid motor associated with the cam follower engaging said first surfaces to said first.

pressure'line as saidfirst surfaces move'into the path of said followers and successively connect' the fluid motor associated with .the cam follower engaging said second surface to said second pressure line as said second surfaces move into the path of said followers.

3; Irradevice of the character described a pair of memberscapable of relative rotation, a cam fixed on one ofsaidrrierhbers provided with a plurality of spaced.

similar first'ramp' surfaces and second similar opposed ramp surfaces inclined in a manner whereby a linear force supplied successively to similar surfaces causes rotation of said one member, a plurality'of fluid motors m'o'unted'onthe other of said members each including an element movable in response to pressure fluid, first and second fluid pressure lines, a cam follower carried by each element adapted to exert said linear force on said surfaces by virtueof said movement of said element, said cam and fluid motors being proportioned so that at least one cam follower is always in engagement with one of said first surfaces and another always in engagement with one of said second surfaces, all of said ramp surfaces being formed so that the ratio between themagnitude' of linear displacement of a cam follower engag ing any ramp surface relative to the magnitude of the annular displacement of said cam is constant, distributor me'ans operated by virtue of the rotation of said one member'operably'connected to said fluid motors to successivelyconnect thefluid motor associated with the cam follower engaging said first surfaces to saidfirst pressure line as said'first surfaces move into the path of saidfollowers and successively connect the fluid motorQ as'sociatedwith the cam' follower engagingsa'id second surface -to"said second pressure line'as said second surfaces move into the path of said followers, and means connecting said pressure lines together through flow restrictionswhereby-rotation of said cam is resisted.

4. An aircraftsteering mechanism comprising'a pair of members capable of relative rotation, a cam fixed on 'tation of said one member, a plur'ality offluid motors mounted on 'tlieother of' said memberskach including an element mgivablc in'res'p'ons'e to pressure fluid, asourc'e of'pres sure'fluid, a fluid reservoir; first and secorid pressure'lines, a'control valve adapted to connect said'first pressure'line'to said source andsaid second pressure'jline to said'rese'rvoir when said control valve is in one'po'si-" tien-andwenneet saidfirst pressure line to said reservoir andsaidsecond pressure lineto said source when said controlvalve is'inanrjther position, a cam follower carriedby' each element adapted to exert said linear force ,9 on said surface by virtue of said movement of said element, said cam and fluid motor being proportioned so that at least one cam follower is always in engagement with one of said first surfaces and another always in engagement with one of said second surfaces, all of said ramp surfaces being formed so that the ratio between the magnitude of linear displacement of a cam follower engaging any ramp surface relative to the magnitude of the annular displacement of said cam is a constant, and distributor means operated by virtue of the rotation of said one member operably connected to said fluid motors to successively connect the fluid motor associated with the cam follower engaging said first surfaces to said first pressure line as said first surfaces move into the path of said followers and successively connect the fluid motor associated with the cam follower engaging said second surfaces to said second pressure line as said second surfaces move into the path of said followers.

5. A steering mechanism comprising a fixed member, a rotatable member mounted for rotation relative to said fixed member, one of said members being formed with a cam having a plurality of lobes symetrically spaced around said one member each lobe providing inclined first group of ramp surfaces and inclined second group ramp surfaces opposed to said first group surface, whereby a linear force applied successively to one group produces relative rotation between said members, a plurality of cylinders mounted on the other of said members aligned with said-ramps, a cooperating piston in each cylinder axially movable relative thereto toward said ramp surfaces in response to pressure fluid, a cam follower on each piston engaging said cam adapted to exert said linear force by virtue of said piston movement with at least one cam follower always in engagement with one of said first group of ramp surfaces, all of said ramp surfaces being formed so that the ratio between the magnitude of linear displacement of a cam follower engaging any ramp surface relative to the magnitude of the annular displacement of said cam is a constant, and at least another of said followers in enaggement with one of said second group ramp surfaces, and means operably connected to said cylinders to successively supply pressure fluid to the cylinder associated with the cam follower engaging said first ramp surfaces as they move into the path of said followers for producing relative rotation between said members in one direction and to successively supply pressure fluid to the cylinder associated with the cam follower engaging said second ramp surfaces as they move into the path of said followers for producing relative rotation between said members in the other direction.

6. A steering mechanism comprising a fixed member, a rotaatble member mounted for rotation relative to said fixed member, one of said members being formed with a cam having a plurality of lobes each providing similar inclined first ramp surfaces and similar inclined second ramp surfaces opposed to said first surface, whereby a linear force applied successively to similar surfaces produces relative rotation between said members, a plurality of cylinders mounted on the other of said members aligned with said ramps, a cooperating piston in each cylinder axially movable relative thereto toward said ramp surfaces in response to pressure fluid, a cam follower on each piston engaging said cam adapted to exert said linear force by virtue of said piston movement with at least one cam follower always in engagement with one of said first ramp surfaces and at least another of said followers in engagement with one of said second ramp surfaces, all of said ramp surfaces being formed so that the ratio between the magnitude of linear displacement of a cam follower engaging any ramp surface relative to the magnitude of the annular displacement of said cam is a constant, and means operably connected to said cylinders to successively supply pressure fluid to the cylinder associated with the cam follower engaging said first ramp surfaces as the surfaces move into the path of said followers for producing relative rotation between said members in one direction and to successivly supply pressure fluid to the cylinder associated with the cam'follower engaging said second ramp surfaces as such surfaces move into the path of said followers for producing relative rotation between said members in the other direction.

References Cited in the file of this patent UNITED STATES PATENTS 1,228,502 Vance June 5, 1917 2,423,701 Hardy July 8, 1947 2,424,233 Greenough July 22, 1947 2,545,774 Griswold Mar. 20, 1951 2,621,002 Pittman Dec. 9, 1952 r 2,712,422 Gerwig July 5, 1955 2,759,687 Hogan Aug. 21, 1956 FOREIGN PATENTS 2,625 Great Britain May 25, 1910 

